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Full text of "Hacks and Mods"

LED Starry Sky 



.1 



Make Projects 



build, hack, tweak, share, discover. 



LED Starry Sky 

Written By: Igisha 



SUMMARY 

A starry sky is a sight that leaves no one indifferent. 

With a little patience and the will, you can make an LED starry sky that will make your space 
extraordinary. 



Step 1 — LED Starry Sky 




• Determine the desired position and 
shape of the starry sky. That may 
be part of the ceiling or the entire 
ceiling. Sketch the surface of the 
starry sky in the appropriate scale, 
and sketch the positions of the 
LEDs. 



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LED Starry Sky 



Step 2 




• Choose the type of material for the background of the starry sky. It could be gypsum 
wallboard, plywood, acrylic or the like. Cut your material into the desired dimensions, 
smooth out any roughness and paint it the color desired. If the material is thicker than 
5mm (this applies to all materials except acrylic), the LEDs are mounted on the outside 
(visible) side. Drill holes for the mounting of the LEDs according to the scheme you have 
outlined. Drill holes 4.5mm in diameter and make sure that the holes have clean edges. 
Drill from the side on which the LEDs will be mounted. 



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LED Starry Sky 



Step 3 




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LED Starry Sky 



• Use LEDs that are 5mm in diameter. The best are the kind with a flat head and a wide 
angle of view. Flat 5mm LEDs fit better on the "sky's" surface, and those with a wide 
viewing angle illuminate the surface around them and give a nice visual effect. 

• Power consumption and supply voltage are also important. LED supply voltage is different 
for different color LEDs. Some standard values are 2V to 2.5V for red and amber 
LEDs, and 2.5V to 3V for white, blue and green. The operating current of standard 5mm 
LEDs is 20-25mA. If you acquired the LEDs and you do not have accurate data for them, 
you can use these figures to calculate the current-limiting resistor with a power adapter as 
will be described. 

• Solder wires to each LED. It is best to use a red wire to connect to the anode and a black 
wire to the cathode for ease of connection later on. The length of the wires will depend on 
the spacing and number of LEDs. You can connect them in groups of a few units and then 
connect the groups to each other. 

• If you do not have an instrument to check the polarity of the LEDs, you can use a 1 .5V 
battery with a red wire connected to the positive ("+") terminal and a black wire connected 
to the negative ("-") terminal. The LED will light up when the positive wire is connected to 
the anode and the black wire to the cathode. Another way to identify the anode and 
cathode is that each LED has a notch on one side. The lead near the notch is the cathode 
and it connects to the negative, i.e., black wire. Also, the longer lead of the LED is the 
anode. 

• The leads should be cut to a length of about 5mm before soldering. The cable should be of 
such thickness that it can freely pass through the hole in the sky background. Solder joints 
should be uniform without excess solder. 

• Insulate the leads from each other with electrical tape. Always use the same length of 
tape. Now thread the cable through the hole; it should pass without getting stuck. Use 
masking tape to secure the wires to the back of the "sky." You can twist the wires and 
create a spiral that will stick in the hole to secure the LED, but do this carefully. You can 
also use glue or silicone to fix the LEDs into the holes. Once you have developed your 
preferred method, installation of the remaining LEDs will go quickly. 



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LED Starry Sky 



Step 4 



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LED Starry Sky 











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• Now the most interesting part of 
this project! How do you make the 
LEDs operate reliably without 
burning out? You need a power 
supply that provides the correct 
voltage and current. 

• At the beginning of the text we said 
that you should know the rated 
current and voltage of your LEDs 
and of course how many LEDs are 
on your starry sky. For example, 
your starry sky has 20 LEDs, with 
the following characteristics: U = 
2.5 V (LED nominal voltage) I = 
25mA (nominal current). First 
determine the current the power 
source has to supply: 20 LEDs x 
0.025 (mA turned into A) = 0.5A = 
500mA. Almost every phone 
charger fulfills this requirement. 

• If you have an old power adapter, 
look at its output characteristics. 
Usually U = 5V, I = 650mA or 
750mA. Remember, the amount of 
current that the adapter can supply 
should be slightly greater than you 
need. This means you will not 
overload the power supply. 

• The next step is to determine the 
resistor that will reduce the 
adapter's voltage to 2.5V or 
whatever the LEDs require. In this 
example, the adapter's original 
voltage is 5V. The calculation is as 
follows: U (resistor) = U (adapter) 
- U (LED) = 5V - 2.5V = 2.5V. R = 

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LED Starry Sky 



U (resistor) / 1 (20 LEDs) = 2.5V / 
0.5A = 5 ohms. Last, it is 
necessary to determine the power 
dissipation of the resistor: P 
(resistor) = U (resistor) x I (20 
LEDs) = 2.5V x 0.5A = 1 .25W. 

• When you purchase your resistor, 
please select one with a greater 
power rating than you calculated 
because it will produce less heat 
and reduce the risk of burning out. 
For example, if you calculate the 
power dissipation as 1.25W, you 
can select a 2W resistor. 

• As for the resistor values in 
ohms, you will not go wrong if you 
select a value 10-15% greater than 
calculated, because this will reduce 
the current through the LEDs and 
prolong their life. Your starry sky 
will shine a little less, but you will 
merely be using it as a decorative 
lighting system. 



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LED Starry Sky 



Step 5 




• All that remains is to mount the starry sky on the ceiling and enjoy. If you need to install a 
power mains outlet near where your sky is mounted, be sure to disconnect the circuit 
when installing the wiring. If you are not an electrician, leave that part to a professional. 
Remember that high voltage is dangerous! Your installation must be safe; use proven 
parts. 

• If you want to use a great many LEDs to create your own starry sky, you can make 
several panels that will connect with each other, but the power supply must provide more 
current and you must use a resistor for each group of LEDs. 

This document was last generated on 2012-11-03 01 :43:51 AM. 



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